Electronic contacting of x-ray generator



P 1955 R. L. WRIGHT, JR 2,719,234

ELECTRONIC CONTACTING OF X-RAY GENERATOR Filed Oct. 21, 1952 WITNESSES: INVENTOR M 57 Fsberi L.Wrigh1,Jr. Cam/v61 %Z6fi% United States Patent ELECTRONIC CONTACTING OF X'RAY GENERATOR Robert L. Wright, Jr., Linthicum Heights, Md., assignor to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Application October 21, 1952, Serial No. 315,878

7 Claims. (Cl. 250-102) My invention relates to electrical circuits and, more particularly, to those circuits wherein power is to be supplied from a conventional alternating current source through an electronic switch or contactor to a load, such as an X-ray tube or generator, at a wide range of voltages.

Ignitron tubes have been used in the past for contacting X-ray generators. In some of these applications of ignitrons-for contacting, a pair of ignitrons are connected inversely in parallel. In such an application of ignitrons for contacting an X-ray generator, the ignitrons are connected in series with the output terminals of an autotransformer, the input terminals of which are connected to a suitable power supply, and the primary winding of a high voltage transformer, the secondary terminals of which are connected through a rectifier to the X-ray tube or generator.

It has been found that the ignitron tubes when used for switching the high voltage source of an X-ray generator are not dependable in operation when the voltage applied between the anode and the cathode electrodes of the ignitrons is lower than 100 volts. On the other hand, it is desired, in such an application of ignitrons that the voltage applied between the anode and cathode electrodes does not exceed 300 volts.

The voltage range of an X-ray generator is wide, for example, 30 to 140 kilovolts, due to the demands and requirements of X-ray technique. Assuming the stepup ratio of a high voltage transformer which supplies the voltage to the X-ray tube is 1 to 500, then to obtain 140 kilovolts across the secondary winding of the high voltage transformer, 280 volts must be applied to the primary winding of the high voltage transformer, while to obtain 30 kilovolts across the secondary winding would require 60 volts on the primary winding. The above figures indicate that the operation of the ignitron tubes would not be dependable on the lower range of the X-ray generator.

In the past when the applied voltage across the anode and cathode electrodes of the ignitron is below 100 volts, a special autotransformer has been connected on the load side of the ignitron tubes and the high voltage transformer connected to the output of the special autotransformer. The operation of the ignitron tubes when used for switching the high voltage in such a circuit was satisfactory, but the expense and the bulk of the additional autotransformer was objectionable.

It is an object of my invention to provide an improved circuit that will obviate the above-mentioned disadvantages of the prior art system for X-ray generators, of which I am aware.

It is a further object to provide an improved circuit of the type in which ignitron tubes are utilized as electron contactors or switches in the primary winding of the high voltage transformer of the power supply for an X-ray generator.

These and other objects are effected by my invention as will be apparent from the following description taken Patented Sept. 27, 1955 in accordance with the drawing throughout which like reference characters indicate like parts, and in which the single figure of the drawing is a schematic showing of a preferred embodiment of my invention.

Referring to the drawings in detail, there is shown a rectifier 18 supplying power to a load which is illustrated as an X-ray tube or generator 17. The rectifier 18 is comprised of four rectifying elements 12 connected in a full wave rectifier bridge. The X-ray tube or generator 17 is connected to the output terminals 13 and 14 of the rectifier 18 while the input terminals 15 and 16 of the rectifier 18 are connected to the secondary winding 19 of a high voltage transformer 20. The high voltage transformer 20 has in addition to the secondary winding 19, two primary windings 21 and 22.

The reference character 24 illustrates a relay having five pairs of contacts 26, 27; 29, 30; 33, 34; 36, 37and 39, 40. Three normally open contact bridging members 31, 35 and 41 and two normally closed bridging members 28 and 38 are carried by a movable member 42, which is attached to an armature 43 of a solenoid having an operating coil 44.

The contacts 27, 30 and 34 of the relay 24 are connected to the upper terminal of the primary winding 21. The contacts 37 and 40 of the relay 24 are connected to the lower terminal of primary winding 21.

The upper terminal of the primary winding 22 is connected to contacts 33 and 36. The lower terminal of the primary winding 22 is connected to contact 39 and to the electronic contactor 94.

Contact 26 is connected to the arm 81 of a series fine adjustment switch 80. Contact 29 is connected to the arm 83 of a parallel fine adjustment switch 82.

An autotransformer 50 is connected to a commercial source of alternating voltage (not shown) by the input leads 51 and 52.

The series fine adjustment switch 80, having a plurality of contacts 1 to 11 and a rotating arm 81 for sweeping over the contacts 1 to 11, is connected to the output of the autotransformer 50. The output terminals 61, 63, 65, 67, 69, 71, 72, 73, 74, and 76 of the autotransformer 50 are connected respectively to the contacts 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 and 11 of the series fine adjustment switch 80.

The parallel fine adjustment switch 82, having a plurality of contacts 1 to 11 and a rotating arm 83 for sweeping over the contacts, is also connected to the output of the autotransformer 50. The output terminals 61 to 71 of the autotransformer 50 are connected respectively to the contacts 1 toll of the parallel fine adjustment switch 82.

A selector switch 84 which selects voltages in steps large compared to switches and 82, is also connected to the output of the autotransformer 50. The switch 84 has a plurality of contacts 1 to 11 and a rotating arm 85 for sweeping the contacts. The output terminals 53, 54, 55, 57 and 59 of the autotransformer 50 are respectively connected to the contacts 1, 2, 3, 5 and 7 of the switch 84, while output terminals 56, 58 and 60 of the autotransformer 50 are respectively connected to the pairs of contacts 4, 9; 6, 10; and 8, 11 ofthe switch 84. The rotating arm 85 of the switch 84 is connected to the electronic switching or contacting circuit 94. p

The electronic switching or contacting circuit 94 comprises two ignitron tubes 95 and 96 connected inversely in parallel; that is, the cathode 97 of the ignitron tube 95 is connected to the plate electrode 99 of the ignitron tube 96 while cathode 100 of ignitron tube 96 is connected to plate electrode 98 of the ignitron tube 95.

The firing voltage is supplied to the make-alive electrodes 101 and 102 by a conventional firing control 104. The firing control 104 supplies voltage to fire the ignitrons 95 and 96. The firing voltage may be applied to or removed from the ignitrons 95 and 96 for any predetermined interval as desired by the operator of the X-ray apparatus or by somev suitable timing mechanism.

The rotating arm 85 of the switch 84' is connected to the cathode 97 of tube 95 and the anode 99 of tube 96. The anode 98- of tube 95', and cathode 100 of the tube 96 are connected to the contact 39 of the relay 24.

The reference character 86 illustrates a cam mounted on the rotating arm 85 of the switch 84. The cam 86 operates a movable member or follower 87 to which a contact bridging element 88 of switch 90 is attached. The switch 90 is comprised of the contact bridging element 88 and a pair of contacts 91 and 92'. The relay coil 44 and a suitable power source 93 are serially connected between the contacts 91 and 92' of the switch 90.

The series fine adjustment switch 80 and the parallel fine adjustment switch 82 are ganged as indicated by the dotted line 110.

In the operation of the circuit, assume a line supply voltage of about 220 volts is applied to the two input lead's 51 and 52 of the autotransformer 50. If the rotating arm 85 be placed on contact 11 of large step voltage switch 84, the voltage selected at terminal 60 of the autotransformer will be 140 volts with reference to terminal 71 of the autotransformer 50. When the large step voltage switch 84 is in this position, the switch contacts 91 and 92 will be open. The contacts 36, 37 and 26, 27 of the relay 24 will be closed by the respective bridging elements 38 and 28. The remaining contacts of the relay 241 will be open.

The circuit from the output of the autotransformer 50 will consist of the large step voltage selector switch 84', the electronic switch or contactor 94, the primary windings 22 and 21 of the high voltage transformer 20, the series fine. adjustment switch 80 all connected in series to the autotransformer 50. With the switch arm 85 on position 11 of the switch 84, the switch arms 81 and 83 of switches 80 and 82 could be in any position.

If the series fine adjustment switch 80 be placed on position 6, with the switch arm 85 of switch 84 on position 11, the voltage across the anode and cathode electrodes of the ignitrons 95' and 96 will be 140 volts which will also be the voltage across the series connected primary windings 21 and 22 of the transformer 20. If the high voltage transformer 20 has a transformation ratio of 1 to 250 when its primary windings 21 and 22 are connected in series, then the voltage across the secondary winding 19 of the high voltage transformer 20 will be 35 kilovolts. j

If the rotating arm 85 of the large step voltage switch 84 is moved to contact 8, the switch 84 will still be connected to the same terminal 60 of the autotransformer 50 as in position 11. The cam 86 will in this position of switch arm 85 engage the movable element 87 and close the contacts 91 and 92 of switch 90. The coil 44' of the relay 24 will be energized by the power source 93 and movable member 42 of the relay 24 will be moved to a position to close pairs of contacts 29, 30; 33, 34; and 39, 40 respectively by the bridging elements 31, 35 and 41, while the other pairs of contacts 26, 27 and 36, 37 will be opened.

The circuit now includes the large step voltage selector switch 84, the electronic switch or contactor 94, the primary windings 21 and 22 of transformer 20 connected in parallel, and the parallel fine adjustment switch 82 which is connected tothe output of the autotransformer 50.

If the parallel fine adjustment switch 82 has its rotating arm 83 on contact 11', when the rotating arm 85 of switch 84 is on contact 8, the voltage across the anodes and cathodes of the ignitron tubes 95 and 96 will be 140 volts. The transformation ratio of the high voltage transformer 20 will now be I to 500 since its primary windings 21 and 22 are in parallel. The voltage across the sec- 4 ondary winding 19 of the high voltage transformer will be- 70 kilovolts.

From the foregoing description taken in connection with the drawing, it is seen that a wide range of voltages are available for the X-ray generator while the voltage across the anode and cathode of the ignitron tubes will be held within the desired range. I have described the circuit with reference to only two settings on the selective voltage switches; however, it is obvious. that a large number of switch settings are available for both series and parallel connection of the primary windings of the high voltage transformer.

While I have shown my invention in only one form it will be obvious to those. skilled in the art that it is not so limited, but is susceptible of various other changes and modifications without departing from the spirit and scope thereof.

I claim as my invention:

1. In a system for supplying electric power to an X-ray generator, the combination comprising an autotransformer having a plurality of output terminals, a high tension transformer having a plurality of primary windings, and having a secondary winding connected to supply anode operating potential to said X-ray generator, an electronic contactor, a relay switch connecting said primary windings in series when in a first position and in parallel when in a second position, a selector switch having fixed contacts connected to certain of said auto-transformer output terminals, and having a movable contact, means connecting said movable contact, said relay switch, and said contactor in series, and means coordinated with said movable contact for actuating said relay switch when said movable contact is moved through a predetermined position.

2'. In a system for supplying electrical power from a variable source to an X-ray generator, the combination comprising, an autotransformer having a plurality of output terminals, a high voltage transformer having two primary windings and a secondary winding, a first switching means connected to said output terminals of said autotransformer for controlling voltage supplied to said primary windings of said high voltage transformer, a second switching means, an electronic contactor connected between said first switching means and second switching means, means connecting said second switching means to the primary windings of said high voltage transformer, and means controlled by said first switching means for operating said second switching means to connect the primary windings of said transformer in series or in parallel.

3. In a system for supplying electrical power from a variable source to an X-ray generator, the combination comprising a high voltage transformer having two primary windings and a secondary winding, an autotransformer having input terminals and a plurality of output terminals, an electronic contactor for exciting said high voltage transformer, a first switching means for selectively connecting appropriate output terminals of said autotransformer in series with said electronic contactor and said primary windings of said high voltage transformer, a second switching means connected between said primary windings of said high voltage transformer and said electronic contactor for connecting said primary windings either in series or in parallel, and an X-ray generator connected to the secondary winding of said high voltage transformer.

4. A power supply circuit for an X-ray generator comprising, an autotransformer, having input and output. con nections, a plurality of controlling switches connected to the output connections of said autotransformer for controlling the output voltage thereof, an electronic contactor connected to one of said controlling switches, a high voltage transformer having a plurality of primary windings and a secondary winding, and a transformer switch con-- necting said primary windings to said electronic contactor, and means coordinated with the position of one of said controlling switches for operating said transformer switch to connect said primary windings'either in parallel or series.

5. An electric system for supplying power to an X-ray tube comprising an autotransformer having input and output terminals, a plurality of voltage selector switches connected to the output terminals of said autotransformer for selecting the output voltage from said autotransformer, an electronic contacting device connected to one of said voltage selector switches, a high voltage transformer having two primary windings and a secondary winding, a transformer switch connected between the primary windings of said high voltage transformer and said electronic contacting device, means under control of one of said voltage selector switches for determining the position of said transformer switch, with the primary windings of said high voltage transformer being connected in series for one position of said transformer switch or in parallel for the other position of said transformer switch, and means connecting a load to said secondary winding of the high voltage transformer.

6. An X-ray power supply comprising in combination, an autotransformer having two input terminals and a plurality of output terminals, a large step voltage selector switch and a plurality of small step voltage selector switches connected to the output terminals of said auto transformer, an electronic contactor, a high voltage transformer having a plurality of primary win-dings and a secondary winding, means connecting said electronic contactor and said primary windings of said high voltage transformer in series between said large step voltage selector switch and one of said small step voltage selector switches, a cam actuated relay switch mounted on said large step voltage selector switch to selectively connect the primary winding of said high voltage transformer in series or in parallel depending upon the position of said large step voltage selector switch.

7. An X-ray power supply comprising an autotransformer with input terminals and output terminals, a plurality of voltage selector switches connected to said output terminals, an ignitron contactor circuit, a high voltage transformer having a plurality of primary windings and a secondary winding, a two position relay switch for connecting said primary windings of said high voltage transformer in series in one position and in parallel in the other position, means connecting said ignitron contactor circuit between one of said voltage selector switches and said relay switch, and means actuating said relay switch to one of its two positions when one of said voltage selector switches is moved through a predetermined portion of its selector range.

References Cited in the file of this patent UNITED STATES PATENTS 2,207,202 La Deau July 9, 1940 2,492,281 Hall Dec. 27, 1949 2,526,390 Moran et al Oct. 17, 1950 

